Manufacture of screw propellers



July 26, 1927. 1, 31,224

H. .LEITNER MANUFACTURE OF SCREW PROPELLERS I Original Filed April 24,1926 Patented July 26, 1927.

UNITED STATES HENRY LEITNEB, OF GROYDON, ENGLAND. v

MANUFACTURE OF SCREW PROPELLERS.

Original application illed April 24, 1928, Serial No. 104,449, and inGreat Britain July 9, 1924.

Divided and this application flied December 8, 1926. Serial No. 153,411.

This invention relates to the manufacture of metal screw-propellers,primaril intended for use on aircraft, the bla es of which may or maynot be detachable and adjustable for pitch.

. In the accompanying diagrammatic drawin Ihgure 1 is a side viewshowing a blank for a propeller blade arranged relatively to 10 the bedof a milling machine and cutter thereof for effecting one of the stagesin the manufacture of the improved blade.

Figure 2 is a view of the cutter at right angles to that shown in Figure1.

Figure 3 is a plan of a blade blank illustrating a modified stage in themanufacture and Figure 4 is a view of two milling cutters therefor.

2 Figure 5 is a view of another milling cutter illustrating anothermodification in the manufacture of a propeller blade.

at is the simple or composite plate or block of metal which is shaped toprovide the working or acting faces of a propeller blade; for instance,the block is faced or machined flat on one side I), which face may ormay not be parallel to the opposite face, and clamped on to the bed a,Figure 1, of a milling machine with the flat face downward, in such amanner that, with reference to the said flat face, the end d, which willultimately be the tip of the blade, is higher than the otherend by aredetermined amount. The flat face may ave been previously cut on thetaper relative to the other or upper face in such a, way that the latteris parallel to the bed of the machine when set up. A straight out orcuts is then taken along the m length of the biock with a shaped millingcutter e, or gang of cutters, acting on the other face f of the blade,the blade being rocked longitudinall by a corresponding movement of thebe 0 asindicated by the dotted lines in Fi ure 1. The milling cutter isshaped to tie largest section of the finished blade, which will belocated at the butt end 9 of the blade. As many cuts as necessary aretaken until the blade is of the required thickness, which thickness willvary from the butt to the ti in direct proportion to the inclination oft e machined face and the roc of the machine bed. The dot and dash lines6 b, in Figure 2, indicate,

and rocking of the machine bed will be determined by the shape of thecutter and the widths of the blade. In either case, the blade will beshaped somewhat like the head of a lance or spear.

An alternative method to that above described is to use the same cutteras described but to cut the blade equal in width and thicknessthroughout its length, and then to plane the face at an inclination tothe back.

Up to this stage I have produced a blade correct in section and track,but without twist, and this latter is provided by the application of atorque.

Instead of shaping the face f of the blade completely at one cut aspreviously described, I may proceed as follows, that is to say, I make acut or cuts in the blade with two or more cutters. As shown in Figure 4,the cutter is shaped as at a to suit the leading edge and a cutter isshaped as at n for the trailing edge of the blade, the position of theblank being re-set after the out or cuts from one edge are made toenable the cut or cuts for the other edge to be made. The path of travelof the cutters may or may not be parallel to each other l id to thecentre line of the resulting blade as seen in plan View. In Figure 3,the dot and dash lines indicate two paths of the cutter out ofparallelism.

An alternative method consists in the use of a single tool such as aplaning or shaping tool. In this case at each successive cut, the toolmust be raised or lowered, relatively to the face of the blade, inaddition to being moved in a transverse direction. ting of the tool canbe arranged by a suit able cam motion or by hand.

If the other side of the blade is required to be curved, it is onlynecessary to reverse the blank and carry out similar operations on thatside.

The rocking of the bed a of the machine with the attached bladerelatively to the tool, may be effected by any suitable cam Thissetmotion or by hand and instead of a longitudinal direction it may berocked in a transverse direction, or in a direction combining these twomovements.

The rockin may be carried out either whilst the too is in motion orduring a temorary pause. Theexpression rocking the bed covers anymovement of the work relatively to the tool other than that of feed andtravel.

Instead of the straight cuts described above, Imay twist or turn theblank longitudinally prior to machining, which twist would enable themost desirable part of the cutter to operate. For example, whenconsidering the tip of the blade as cut by a single cutter e, aspreviously described with reference to Figure 1, the resultant shape israther too thin and shar for practical work, as indicated by the 0t anddash lines 0, Figure 5. If, however, the blank is twisted, advantage canbe taken of the greater camber at one side of the cutter e, the sideroducing the leading edge of the blade, an a better section results,this being indicated by the dot and dash line p, Figure 5.

After one or any combination of the above operations has or have beencompleted, the blade is twisted to. the correct helical twist ashereinbefore described and any forward rake necessary can be impartedeither by a torque or by pressure, preferably, when the material is inits softest state.

Claims:

1. A process of manufacture of a screwpropeller blade from a solid blockor blank of metal of approximately the shape of the blade consisting inmachinin one side of the blank flat, securing the bfink with themachined surface downward on the bed of a shapin machine with the enddesigned to form tie ti of the blade higher than the other end, shapingthe upper surface of the blade by cutters travelling longitudinally ofthe blade and at the same time rocking the blade by a correspondingmovement of the machine bed.

2. A process of manufacture of a screwpropeller blade as claimed inclaim 1, wherein the blade and machine bed are rocked longitudinally.

3. A process of manufacture of a screwpropeller blade as claimed inclaim 1, wherein the blade and machine bed are rocked transversely.

4. A process of manufacture of a screwpropeller blade claimed in claim1, wherein the blade and machine bed are rocked in a direction combininglongitudinal and transverse movements.

5. A modification of the process claimed in claim 1, wherein the blankis twisted prior to the cutting operation to take advantage of thevarying camber of the cutter, and wherein the correct twist for pitch isimparted in a subsequent operation.

6. A process of manufacture of a screw propeller blade from a solidblock or blank of metal of approximately the shape of the blade,consisting in machining one side of the blank flat, securing the blankwith the machined surface downward on the bed of a milling machine withthe end designed to form the tip of the blade higher than 'the otherend, shaping the upper surface of the blade by milling) cutterstravelling longitudinally of the lade and at the same time rocking theblade by a corresponding movement of the machine bed.

HENRY LEITNER.

